Many types of invertible pumps are known, such as those described in U.S. Pat. No. 5,222,636, U.S. Pat. No. 4,775,079, U.S. Pat. No. 4,277,001, U.S. Pat. No. 5,738,252, EP-A-0648545 and EP-A-1029597, however such pumps have serious drawbacks which limit their production and use. In this respect, some are of very complex structure with many component parts difficult to mould and assemble; others entrust the seal to small, light sleeves slidable on the surfaces of a holed cylindrical body, the mobility of such sleeves being very precarious and unreliable; still others are of considerable size below the seal gasket of the ring cap for fixing the pump onto the mouth of a liquid container, either axially (see the two said European patents and U.S. Pat. No. 4,277,001 and U.S. Pat. No. 4,775,079) or transversely (U.S. Pat. No. 5,222,636), making them unsuitable for use on small dimension containers such as those required, for example, in the perfumery field.
The operation of an invertible pump depends on the fact that the liquid enclosed in a container must be able to penetrate into the pump compression chamber by rising along a dip tube (of which one end is mounted on the pump and the other end is free and is positioned in proximity to the container base) when the pump is upright above the container, but to penetrate directly into said compression chamber from a hole provided in the pump body, and of which the opening is controlled by a unidirectional valve which opens only during pump intake and only when the pump is inverted, i.e. positioned below the container.